Current-Driven Skyrmion Dynamics and Drive-Dependent Skyrmion Hall Effect in an Ultrathin Film

Roméo Juge, Soong-Geun Je, Dayane de Souza Chaves, Liliana D. Buda-Prejbeanu, José Peña-Garcia, Jayshankar Nath, Ioan Mihai Miron, Kumari Gaurav Rana, Lucia Aballe, Michael Foerster, Francesca Genuzio, Tevfik Onur Mentes, Andrea Locatelli, Francesco Maccherozzi, Sarnjeet S. Dhesi, Mohamed Belmeguenai, Yves Roussigné, Stéphane Auffret, Stefania Pizzini, Gilles Gaudin, Jan Vogel, and Olivier Boulle

Phys. Rev. Applied 12, 044007 – Published 3 October 2019

Abstract

Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their current-induced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of Néel skyrmions with diameters in the 100-nm range in an ultrathin $Pt$ / $Co$ / $Mg O$ trilayer. We find that these skyrmions can be driven at a speed of $100 m s^{- 1}$ and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties.

Received 24 June 2019
Revised 31 August 2019
Corrected 11 August 2020

DOI:https://doi.org/10.1103/PhysRevApplied.12.044007

Physics Subject Headings (PhySH)

Ferromagnetism Hall effect Skyrmions Spintronics

Magnetic multilayers

Micromagnetic modeling X-ray photoemission electron microscopy

Condensed Matter, Materials & Applied Physics

Corrections

11 August 2020

Correction: The units for the last two columns in Table 1 were incomplete and have been fixed.

Authors & Affiliations

Roméo Juge ^1,*, Soong-Geun Je ¹, Dayane de Souza Chaves², Liliana D. Buda-Prejbeanu¹, José Peña-Garcia², Jayshankar Nath¹, Ioan Mihai Miron¹, Kumari Gaurav Rana¹, Lucia Aballe³, Michael Foerster³, Francesca Genuzio⁴, Tevfik Onur Mentes ⁴, Andrea Locatelli⁴, Francesco Maccherozzi⁵, Sarnjeet S. Dhesi⁵, Mohamed Belmeguenai⁶, Yves Roussigné⁶, Stéphane Auffret¹, Stefania Pizzini², Gilles Gaudin¹, Jan Vogel², and Olivier Boulle ^1,†

¹Univ. Grenoble Alpes, CNRS, CEA, Grenoble INP,‡ IRIG-Spintec, 38000 Grenoble, France
²Univ. Grenobles Alpes, CNRS, Institut Néel, 38000 Grenoble, France
³ALBA Synchrotron Light Facility, 08290 Cerdanyola del Vallès, Barcelona, Spain
⁴Elettra-Sincrotrone Trieste S.C.p.A., 34149 Basovizza, Trieste, Italy
⁵Diamond Light Source Ltd., Didcot OX11 0DE, United Kingdom
⁶Laboratoire des Sciences des Procédés et des Matériaux, CNRS, Université Paris 13, 93430 Villetaneuse, France

^*romeo.juge@protonmail.com
^†olivier.boulle@cea.fr
^‡Institute of Engineering Univ. Grenoble Alpes

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Vol. 12, Iss. 4 — October 2019

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Images

Figure 1
(a) A scanning electron microscopy (SEM) image of the device, consisting of a 3- $µ m$ -wide $Pt$ / $Co$ / $MgO$ track contacted with $Ti$ / $Au$ pads for the current injection. A XCMD-PEEM image (black dashed rectangle) showing isolated skyrmions in the track is superimposed on the SEM image. (b)–(e),(f)–(j) Two distinct sequences of images. Each image is acquired after a single 11-ns current pulse. In both cases, the charge current is flowing along $+ \hat{x}$ with $J = 5.6 \times 10^{11} A m^{- 2}$ . The applied magnetic field is $µ_{0} H_{z} ˜ - 5 mT$ .
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Figure 2
(a)–(c) A sequence of XMCD-PEEM images showing a skyrmion after two consecutive 8-ns current pulses with opposite polarities (the scale bar is 200 nm). The skyrmion Hall angle (SkHA) $T_{SkH}$ is defined as the angle between the current and the skyrmion-motion directions. (d) The skyrmion velocity as a function of the current density. (e) The SkHA as a function of the skyrmion velocity. The red solid lines and red dashed lines are the analytical skyrmion velocity and the SkHA calculated from Eqs. (2) and (3) using the parameters given in Table 1 for $a = 0.43$ and $a = 0.30$ , respectively. The error bars denote the sum of the systematic measurement error and the standard deviation. The shaded areas highlight the regime for which no significant displacement is observed after a single current pulse.
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Figure 3
(a),(b) Sequences of snapshots showing the current-driven dynamics of a skyrmion in an ideal disorder-free film with (a) $J = 2.9 \times 10^{11} A m^{- 2}$ and (b) $J = 6.7 \times 10^{11} A m^{- 2}$ (the scale bar is 100 nm). (c) The evolution of the skyrmion size as a function of the applied current density (at 5 ns). The size is defined as the area for which $m_{z} > 0$ (in red), normalized by the area at rest. (d) A sequence of snapshots in a disordered film. The dark grains are region of higher anisotropy and the bright grains those of lower anisotropy. (e),(f) A summary of the trajectories recorded for different grain distributions for (e) $J = 2.9 \times 10^{11} A m^{- 2}$ and (f) $6.7 \times 10^{11} A m^{- 2}$ . The blue dotted lines indicate the skyrmion trajectories in the disorder-free scenario. The position of deformed skyrmions is defined as that of their barycenter. The simulations are performed for the experimental parameters listed in Table 1 with the applied field $µ_{0} H_{z} = - 5.4 mT$ .
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Figure 4
(a) The skyrmion velocity as a function of the current density in the case of a disorder-free film (blue circles) and in the case of a disordered film (black stars). (b) The SkHA $T_{SkH}$ as a function of the skyrmion velocity. The analytical solutions (red solid lines) are calculated from (a) Eq. (2) and (b) Eq. (3) using the parameters given in Table 1. To mimic the experimental conditions, the velocity and the SkHA are calculated from the total skyrmion displacement within an 8-ns time window. The error bars denote the standard deviation. The shaded areas highlight the pinned regime.
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